Blends of linear low density ethylene copolymers

ABSTRACT

Novel polymer blends are provided comprising a linear low density copolymer of ethylene with an olefin containing 4 to 10 carbon atoms (LLDPE) compounded with minor amounts of an at least partially isotactic, partially crystalline butene-1 polymer comprising at least about 80 wt. % of polymerized butene-1, and an ABS resin. The blends can be fabricated with better processability into blown films having improved impact and MD tear resistance properties.

CROSS-REFERENCED TO RELATED APPLICATIONS

This application is a continuation-in-part of applications Ser. No.266,957, filed Nov. 3, 1988 and a continuation-in-part of Ser. No.295,430, filed Jan. 10, 1989.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel compositions comprising a linear lowdensity copolymer of ethylene and a minor amount of an olefin containing4 to 10 carbon atoms (LLDPE), and to films of improved properties formedfrom such compositions. Also included in the invention is the process offorming blown films from such compositions which is accomplished withimproved processability.

2. Description of Related Art

The following information is disclosed in accordance with the terms of37 CFR 1.56, 1.97 and 1.98.

U.S. Pat. No. 4,565,847, issued Jan. 21, 1986 to S. K. Bahl et al.,discloses blends of LLDPE, polypropylene (PP) or ethylene-propoylenecopolymer, and ethylene-propylene-diene monomer rubber (EPDM), which arestated to form films having improved MD tear strength and dart dropimpact properties.

U.S. Pat. No. 4,579,912, issued Apr. 1, 1986 to P. J. Canterino et al.,teaches blends of LLDPE and an aromatic polymer, e.g., polystyrene,which are stated to form films of improved MD tear strength and higherstiffness compared to LLDPE alone.

U.S. Pat. No. 4,657,982, issued Apr. 14, 1986 to A. K. Breck et al.,discloses film-forming blends of a linear copolymer of ethylene and a C₄to C₈ alpha-olefin, and two "polybutenes," one having a number averagemolecular weight of 500 to 1500 and the other a number average molecularweight of 1700 to 10,000.

U.S. Pat. No. 4,456,660, issued June 26, 1984 to E. A. Columbo, teachesblends of conventional branched low density polyethylene (LDPE) andpolybutene-1 used to prepare laminated films with unblended LPDE whichare stated to be tough and to have good tear resistance.

U.S. Pat. No. 3,660,530 issued May 2, 1972 to Hoblit et al., disclosesblends of high density polyethylene and block copolymers of polyethyleneand a polymer of butene-1 which are stated to have improved stress crackresistance.

U.S. Pat. No. 4,430,476, issued Feb. 7, 1984 to Liu, discloses theimprovement of the impact resistance and ductility of notchedpolycarbonate resin articles by blending the polycarbonate with varyingamounts of an alkenyl aromatic copolymer, e.g., an ABS resin, and anLLDPE.

Romanian Patent No. 63,726 of Petraru et al., published June 30, 1978[abstracted in C.A. 91(24)194203r] discloses blends of 100 parts of lowdensity polyethylene, 2 to 20 parts of the ABS copolymer, and 10 to 15parts of carbon black extruded into films with transverse andlongitudinal tensile strengths of 160 and 151 kg/cm², tear strength of86 and 84 kg/cm², and breaking elongations of 640 and 660% respectively.

Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, Vol.1., Wiley-Interscience, 1981, pages 442 to 445, and Hawley, CondensedChemical Dictionary, Tenth Edition, Van Nostrand Reinhold, 1981, page 3,describe typical ABS resins contemplated under this invention.

Pending parent application Ser. No. 266,957, filed Nov. 3, 1988discloses and claims blends of LLDPE and a minor amount of a butene-1polymer which can be formed into films having improved impactproperties.

Pending parent application Serial No. 295,430, filed Jan. 10, 1989discloses and claims blends of LLDPE and a minor amount of an ABS resinwhich can be formed into films having improved antiblocking, impact andMD tear resistance properties.

SUMMARY OF THE INVENTION

In accordance with this invention, novel polymer blends are providedcomprising a major amount of a linear low density copolymer of ethylenewith an olefin containing 4 to 10 carbon atoms (LLDPE), compounded withminor amounts of an at least partially isotactic, partially crystallinebutene-1 polymer comprising at least about 80 wt. % of polymerizedbutene-1, and an "ABS resin" as the latter term is understood in the artand as defined hereinafter, based on the total polymer content of theblend. The blends can be fabricated with better processability intoblown films having improved impact and MD tear resistance properties.

DESCRIPTION OF PREFERRED EMBODIMENTS

The linear low density ethylene copolymers (LLDPE) of this invention arelinear copolymers of ethylene and a minor amount, preferably about 2 to10 wt. %, of an olefin, preferably a 1-olefin, containing 4 to 10 carbonatoms and having a density of about 0.9 to 0.94, a melting point ofabout 110° to 130° C., and a melt index of about 0.2 to 10. Thepreferred olefin comonomers are 1-butene, 1-hexene and 1-octene. TheLLDPE may be prepared by any of various methods known in the art, e.g.,by relatively low pressure methods as disclosed, for example, in U.S.Pat. No. 4,076,698, or by relatively high pressure methods, asdisclosed, for example, in U.S. Pat. Nos. 4,405,774 and 4,530,983.

The butene-1 polymers contemplated under this invention are at leastpartially isotactic, partially crystalline polymers comprising at least80 wt. %, preferably at least 90 wt. % of polymerized butene-1. Thesepolymers include homopolymers of butene-1 and copolymers of at leastabout 80 wt. % of butene-1 and up to about 20 wt. % of at least onepolymerized comonomer, e.g., an olefin, preferably a 1-olefin,containing 2 to about 10 carbon atoms, and preferably have a numberaverage molecular weight of at least about 25,000, a density of fromabout 0.890 to 0.920, and a melt index of from about 0.1 to 40, (ASTMcondition E). Some of these polymers are described in the article on"Polymers of Higher Olefins" in Kirk-Othmer, Encyclopedia of ChemicalTechnology, Third Edition, Wiley-Interscience, 1981, pages 470-477. Thepolymers may be prepared using a Ziegler-Natta type catalyst asdescribed for example in U.S. Pat. No. 3,362,940 or the foregoingKirk-Othmer article. In general, the butene-1 polymers in unblended formare capable of being formed into shaped articles such as films.

The "ABS resin" contemplated under this invention comprises a rubbery orelastomeric butadiene polymer dispersed in a rigid or glassystyrene-acrylonitrile copolymer matrix. Preferably, the rubberybutadiene polymer contains, at various points along its backbone,grafted segments of styrene-acrylonitrile copolymer, which have theeffect of improving compatability between the two polymer phases. Alsocontemplated within the term "ABS resin" are physical blends of arubbery butadiene polymer containing no grafted polymer segmentsdispersed in a rigid styrene-acrylonitrile copolymer phase. Generally,there is some degree of cross-linking within the rubbery butadienepolymer phase.

The rubbery butadiene polymer independent of any grafted polymersegments which may be present, usually contains at least about 60 wt. %of polymerized butadiene. Some examples of these polymers arepolybutadiene (a butadiene homopolymer), and copolymers of butadiene andacrylonitrile and/or styrene. The rubbery butadiene polymer may bepresent, for example, in an amount of about 10 to 30 wt. % of the totalpolymer content of the ABS resin, and the overall amounts of polymerizedacrylonitrile, butadiene, and styrene in the ABS resin are within theweight percent ranges of about 15-25:5-25:80-30, respectively,preferably about 15-22:7-40:78-38.

The ABS resins contemplated under the invention may have, for example, a3.2 mm notched Izod impact strength at 23° C. of about 2 to 12 ft-lb/in(ASTM D256), a tensile strength at 23° C. of about 4800 to 7500 psi(ASTM D638), a tensile modulus at 23° C. of about 2.5 to 3.8×10⁵ psi(ASTM D638), a Rockwell hardness at 23° C. of about 88 to 110 HRC (ASTMD785), a specific gravity at 23° C. of about 1.02 to 1.06 (ASTM D792), athermal deflection temperature of annealed samples at 264 psi of about93° to 112° C. (ASTM D648), and a linear coefficient of thermalexpansion of 6.5 to 11.0×10⁻⁵ cm/cm/°C. (ASTM D696). Some suitable ABSresins for use in the compositions and processes of this invention aredescribed in the previously cited Kirk-Othmer and Hawley references, theentire disclosures of which are incorporated by reference.

The blends of LLDPE, butene-1 polymer, and ABS resin may be preparedusing any of various methods known in the art. For example, pellets ofthe three polymers may be dry blended and the blend added directly to ablown film extruder, e.g., a Sterling extruder, to produce films havinga thickness, for example, of about 0.5 to 5 mils.

The polymer blends of this invention contain a major amount, i.e., over50 wt. % of the LLDPE and a minor amount, i.e., under 50 wt. % of thecombination of butene-1 polymer and ABS resin based on the total polymercontent. Preferably, the blend contains about 1 to 20 wt. % each, morepreferably, about 1 to 10 wt. % each of the butene-1 polymer and ABSresin, based on the total polymer content. Moreover, the polymer contentof the blend preferably consists of the LLDPE, butene-1 polymer, and ABSresin. In addition to the polymer components, the blend may also containany of various additives conventionally added to polymer compositionsfor different purposes, e.g., antiblocking agents such as microtalc,stabilizers, compatibilizers, pigments, etc.

The following examples further illustrate the invention.

COMPARATIVE EXAMPLES A TO F AND EXAMPLES 1 AND 2

Films of 1.0 and 1.5 mils nominal gauge thickness were prepared from afirst lot of Mobil NTA-101 LLDPE, which is a linear low densitycopolymer of ethylene and about 6 wt. % of 1-hexene having a density ofabout 0.918, a melting point of about 125° C. and a melt index of about1, blended with 5000 ppm of microtalc as an antiblocking agent(Comparative Examples A and B); the foregoing LLDPE blended with 5 wt. %of Shell PBO400 polybutene-1 (a butene-1 homopolymer) having a densityof about 0.915, a melt index of about 20, and a number average molecularweight of about 40,000, and 5,000 ppm of microtalc (Examples C and D);the foregoing LLDPE blended with 5 wt. % of Cycolac DFA-R1000 mediumimpact ABS resin manufactured by Borg-Warner Chemicals, Inc. andcontaining 20 wt. % of acrylonitrile, 10 wt. % of butadiene, and 70 wt.% of styrene, as determined by ¹³ C NMR, and having a notched Izodimpact strength at 23° C. of about 4.0 ft-lb/in, a tensile strength at23° C. of about 6,200 psi, a tensile modulus at 23° C. of about 3.4×10⁵psi, a Rockwell hardness at 23° C. of about 108 HRC, a specific gravityat 23° C. of about 1.04, a thermal deflection temperature of annealedsamples at 264 psi of about 94° C., and a linear coefficient of thermalexpansion of about 8.8×10⁻⁵ cm/cm/°C., using the ASTM test methodsidentified previously (Examples E and F); and the foregoing LLDPEblended with 5 wt. % of the foregoing polybutene-1 and 5 wt. % of theforegoing ABS (Examples 1 and 2).

The polymer blends of these examples were prepared by dry blending thepolymer pellets and the microtalc powder where used, and the wt. % ofpolybutene-1 and ABS resin in these blends was based on the combinedweight of the total polymers present.

The films were made in a 21/2 inch Sterling blown film extruder underthe following fabrication conditions: BUR (blow up ratio) of 2.5;production rate of 150 lb/hr; die gap of 80 mils; and a 6 inch die.

Table I shows the screw tip pressure and screw amperes at which theextruder operated, and the Induced Blocking Force (ASTM D3354), MD tear(ASTM D1922), Spencer Impact (ASTM D3420), and Dart Drop F₅₀ Impact(ASTM D1709), of the films prepared in these examples.

                                      TABLE I                                     __________________________________________________________________________         Screw                        Dart                                             Tip      Nominal                                                                            Induced   Spencer                                                                            Drop                                             Press.                                                                            Screw                                                                              Gauge                                                                              Blocking                                                                           MD Tear                                                                            Impact                                                                             F.sub.50                                    Example                                                                            psig.                                                                             Amperes                                                                            mils gms  g/mils                                                                             gms/mil                                                                            gms                                         __________________________________________________________________________    A    3090                                                                              46   1.0  85.1 335   763 175                                         B    3090                                                                              46   1.5  75.6 388   633 238                                         C    2680                                                                              29.5 1.0  63.0 405  1770 210                                         D    2680                                                                              29.5 1.5  40.0 510   924 256                                         E    2810                                                                              42   1.0  74.5 435  1860 336                                         F    2810                                                                              42   1.5  84.9 487  1340 404                                         1    2470                                                                              30   1.0  82   522  2030 248                                         2    2470                                                                              30   1.5  75.2 592  1640 360                                         __________________________________________________________________________

EXAMPLES G, H AND 3

In these examples, films of 1.0 mil nominal gauge thickness wereprepared from a second lot of Mobil NTA-101 LLDPE which had beenpremixed with 5000 ppm of microtalc (Example G); the same premixed LLDPEblended with 5 wt. % of the same polybutene-1 as that employed inExamples C, D, 1 and 2 (Example H); and the same premixed LLDPE blendedwith 5 wt. % of the same polybutene-1 as previously employed and thesame ABS resin as employed in Examples E, F, 1 and 2 (Example 3). Thesame procedures as those utilized in the previous examples were employedin preparing the polymer blends and films and in determining theproperties of the films. The results are shown in Table II.

                  TABLE II                                                        ______________________________________                                               Screw                            Dart                                         Tip               Induced        Drop                                         Press.   Screw    Blocking                                                                              MD Tear                                                                              F.sub.50                              Example                                                                              psig.    Amperes  gms     g/mils gms                                   ______________________________________                                        G      2690     42       68      277    144                                   H      2640     30       47      279    163                                   3      2390     28.5     21      412    254                                   ______________________________________                                    

The results shown in Tables I and II indicate that improved MD Tear andSpencer Impact properties were obtained with the films containing bothpolybutene-1 and ABS (Examples 1 to 3) as compared with films of equalthickness containing no polybutene-1 or ABS or containing only one ofthese polymer additions (Examples A to H) whether or not a microtalcantiblocking agent was also present. The results also indicate thatbetter Dart Drop Impact properties and, when microtalc was present inthe films, better Induced Blocking properties were obtained when thefilms contained both polybutene-1 and ABS than when the films containedneither of these polymer additives or only polybutene-1.

Finally, the results show that these properties were accompanied by asuperiority of processability in producing the films of Examples 1 to 3containing both polybutene-1 and ABS as compared with the films ofComparative Examples A to H containing neither or only one of thesepolymer additives, as indicated by lower values of screw tip pressureand screw amperes.

I claim:
 1. A polymer blend comprising a linear low density copolymer ofethylene with an olefin containing 4 to 10 carbon atoms and minoramounts of an at least partially isotactic, partially crystallinebutene-1 polymer comprising at least about 80 wt. % of polymerizedbutene-1, and an ABS resin, based on the total polymer content of theblend.
 2. The blend of claim 1 wherein said ethylene copolymer containsabout 2 to 10 wt. % of said olefin in polymerized form.
 3. The blend ofclaim 1 wherein said olefin is a 1-olefin.
 4. The blend of claim 3wherein said 1-olefin is 1-butene, 1-hexene, or 1-octene.
 5. The blendof claim 1 wherein said ethylene copolymer has a density of about 0.9 to0.94, a melting point of about 110° to 130° C., and a melt index ofabout 0.2 to
 10. 6. The blend of claim 1 wherein said butene-1 polymerhas a number average molecular weight of at least about 25,000.
 7. Theblend of claim 6 wherein said butene-1 polymer is a homopolymer ofbutene-1.
 8. The blend of claim 6 wherein said butene-1 polymer is acopolymer of butene-1 and ethylene.
 9. The blend of claim 1 wherein saidbutene-1 polymer has a density of from about 0.890 to 0.920 and a meltindex of from about 0.1 to
 40. 10. The blend of claim 1 containing about1 to 20 wt. % each of said butene-1 polymer and ABS resin, based on theweight of the total polymer content.
 11. The blend of claim 10 whereinsaid butene-1 polymer and ABS resin are present each in an amount of 1to 10 wt. % based on the weight of the total polymer content.
 12. Theblend of claim 1 in which the polymers present consist of said lowdensity copolymer of ethylene, butene-1 polymer and ABS resin.
 13. Afilm composed of the blend of claim
 1. 14. A film composed of the blendof claim
 4. 15. A film composed of the blend of claim
 11. 16. A filmcomposed of the blend of claim 12.